In a bowl, mix soy sauce, brown sugar, sesame oil, garlic, and ginger.
Add the sliced beef to the marinade and let it sit for at least 10 minutes.
Heat a skillet over medium-high heat.
Add the marinated beef to the skillet in a single layer.
Cook for about 3-4 minutes until browned, stirring occasionally.
Prepare the cooked rice in bowls.
Layer the cooked rice with the beef slices.
Top with sliced cucumbers and green onions.
Drizzle with additional sauce and sprinkle sesame seeds before serving.